The candle power of a lamp placed normal to a working plane is 40 candle power. Find the distance if the illumination is 10 lux

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SSC JE Electrical 10 Oct 2023 Shift 2 Official Paper-I

Answer 1

Concept:

Illumination is defined as the luminous flux received by the surface per unit area.

It is usually denoted by the symbol ‘E’ and is measured in lux or lumen/m2 or meter candle or foot candle.

Illumination, \(E = \frac{\phi }{A} = \frac{{CP \times \omega }}{A}lux\)

Solid angle \(\omega = \frac{A}{{{d^2}}}\)

Illumination \(E = \frac{{CP}}{{{d^2}}}lux\)

Calculation:

Given that, candle power (CP) = 40 CP

Illumination (E) = 10 lux

⇒ 10 = 40/d2

⇒ d = 2 m